1586 CRUSTACEA. 



tinuous line of coast and no intermediate temperature rendering 

 such a transfer impossible; and the passage farther south to the 

 Canaries of several of the species is not beyond what this cause might 

 accomplish. Still, it cannot be asserted that in all instances the dis- 

 tribution here is owing to migration ; nor will it be admitted unless 

 other facts throw the weight of probability on that side. 



IX. But when we find the same Temperate zone species occurring 

 in distant provinces, these provinces having between them no water 

 communication except through the Torrid or Frigid zone, and offering 

 no ground for the supposition that such a communication has existed 

 during the recent epoch, we are led to deny the agency of voluntary 

 or involuntary migration in producing this dissemination. An 

 example of this, beyond all dispute, is that of the Mediterranean Sea 

 and Japan. No water communication for the passage of species can 

 be imagined. An opening into the Red Sea is the only possible point 

 of intercommunication between the two kingdoms; but this opens 

 into the Torrid zone, in no part of which are the species found. The 

 two regions have their peculiarities and their striking resemblances ; 

 and we are forced to attribute them to original creation and not inter- 

 communication. 



X. The resemblances found are not merely in the existence of a 

 few identical species. There are genera common to the two seas that 

 occur nowhere else in the Oriental kingdom, as Latreillia, Ephyra, 

 Sicyonia, &c; and species where not identical have an exceedingly 

 close resemblance. 



Now this resemblance in genera and species (without exact identity 

 in the latter) is not explained by supposing a possible intercommuni- 

 cation. But we may reasonably account for it on the ground of a 

 similarity in the temperature and other physical conditions of the 

 seas ; and the well-known principle of " like causes, like effects" forces 

 itself upon the mind as fully meeting the case. Mere intercommuni- 

 cation could not produce the resemblance ; for just this similarity of 

 physical condition would still be necessary. And where such a simi- 

 larity exists, creative power may multiply analogous species; we 

 should almost say, must, for, as species are made for the circumstances 

 in which they are to live, identical circumstances will necessarily 

 imply identity of genera in a given class, and even of specific structure 

 or of subgenera. 



If, then, the similarity in the characters of these regions is the 



